<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style type="text/css">
        .demo {
            width: 700px;
            height: 1000px;
            border: 50px dotted orange;
            margin: 0 auto;
            background: green url("img/dog.png") no-repeat top center fixed;
        }
    </style>
</head>
<body>
    <div class="demo">
    </div>
</body>
</html>